WASHINGTON — The decision by Deputy Attorney General Rod J. Rosenstein to appoint the former F.B.I. director Robert S. Mueller III as special counsel for the criminal investigation into Russia’s interference in the 2016 election has transformed the inquiry and increased the potential risk it poses to the Trump administration.
Mr. Rosenstein, who was overseeing the investigation because Attorney General Jeff Sessions recused himself, had resisted pressure to take that step. But recent events — including President Trump’s firing of James B. Comey as F.B.I. director, in which Mr. Rosenstein played a role — made that resistance increasingly untenable.
Here is what the appointment means.
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What will be within Mr. Mueller’s jurisdiction?
Mr. Rosenstein’s letter gave Mr. Mueller the authority to look into not only links or coordination between Russia and Trump campaign officials, but also “any matters that arose or may arise directly from the investigation.” And it included a reference to a Justice Department regulation that permits special counsels to investigate attempts to impede their inquiry — like obstruction of justice and witness intimidation.
That mandate would seemingly give Mr. Mueller a writ, if he wants, to investigate whether Mr. Trump’s interactions with Mr. Comey amounted to obstruction of justice.
Given the circumstances, “he is required to look” at whether there was obstruction of justice, said Julie O’Sullivan, a former federal prosecutor who teaches criminal law at Georgetown University. “He can’t ignore this.”
Discussion of that possibility has spiked since Mr. Trump fired Mr. Comey. The president told NBC News that he had been thinking about his dissatisfaction with the Russia investigation when he decided to fire Mr. Comey, and seemingly threatened him in a Twitter post, saying Mr. Comey “better hope” there were no tapes of their conversations. And in a February memo, Mr. Comey recounted Mr. Trump’s pressuring him to drop the related investigation into Michael T. Flynn, the former national security adviser.
What is a special counsel?
Normally, United States attorneys directly oversee criminal investigations, working with the head of the Justice Department’s National Security Division in counterintelligence matters. But their decisions are subject to the oversight and control of the attorney general. In cases that raise questions about high-ranking executive branch officials, the attorney general — and here, Mr. Rosenstein is acting in that role — can appoint a special counsel to run a particular investigation with greater autonomy from the president’s political appointees.
Is Mr. Mueller fully independent of the administration?
No. Many people, including members of Congress, have been calling for an independent criminal investigation. But the central attribute that makes an official completely independent of the White House — protection from being fired at the president’s direction — is no longer legally possible for a prosecutor.
After the Watergate scandal, when President Richard M. Nixon ordered the firing of the Watergate prosecutor as part of the so-called Saturday Night Massacre, Congress created a law that permitted the appointment of an investigator to look into high-level executive branch wrongdoing. An investigator in this role — initially called a special prosecutor and later called an independent counsel — was subject to the control of a panel of judges and could not be fired by the president.
While the Supreme Court upheld this as constitutional, critics said it allowed the prosecutor to run amok. Republicans learned to hate the arrangement during the Iran-contra investigation into the Reagan administration, and Democrats did, as well, during the Whitewater and Monica Lewinsky investigations into President Bill Clinton. When the law expired in 1999, Congress did not renew it.
What autonomy does a special counsel have?
The Justice Department’s regulation gives such a prosecutor a much longer leash than a regular one, but the counsel’s discretionary powers still have limits.
“The special counsel shall not be subject to the day-to-day supervision of any official of the department,” the regulation states. “However, the attorney general may request that the special counsel provide an explanation for any investigative or prosecutorial step, and may after review conclude that the action is so inappropriate or unwarranted under established departmental practices that it should not be pursued.”
If such a situation arises, Mr. Rosenstein must notify Congress, and the regulation gives him the authority to fire Mr. Mueller. And although Mr. Rosenstein’s letter says Mr. Mueller is authorized, if he believes it is necessary and appropriate, “to prosecute federal crimes arising from the investigation of these matters,” it also says he is subject to the special counsel regulations.
Could Mr. Rosenstein go further in shielding Mr. Mueller?
Yes. There is precedent for granting special counsels greater autonomy than the regulation calls for — and, in a coincidence, it involves Mr. Comey. In 2003, as the deputy attorney general in the George W. Bush administration, Mr. Comey was overseeing an investigation into the leaking of the identity of a C.I.A. operative, Valerie Plame Wilson, because the attorney general, John Ashcroft, was recused.
Mr. Comey appointed Patrick Fitzgerald, the sitting United States attorney in Chicago, as special counsel. As part of that move, he waived the regulation and delegated his supervisory powers as acting attorney general for the case to Mr. Fitzgerald, giving him greater autonomy to make decisions about subpoenaing witnesses or bringing charges without the potential for second-guessing by Mr. Comey.
But Mr. Rosenstein did not take that step for Mr. Mueller.